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New classical and non-classical hydrides of Ru(II) in aqueous solution

Gábor Papp 1,  Gabor Laurenczy 2,  Ferenc Joó 3

1. Research Group of Homogeneous Catalysis, Hungarian Academy of Sciences, 1, Egyetem tér, Debrecen H-4010, Hungary
2. EPFL, Istitut de Sciences et Ingénierie Chimiques, LCOM, Lausanne CH-1015, Switzerland
3. University of Debrecen, Institute of Physical Chemistry, POB 7, Debrecen H-4010, Hungary

Abstract

We have described earlier that the selectivity of the hydrogenation of cinnamaldehyde catalyzed by the water soluble complex [{RuCl2(mtppms)2}2] (+ mtppms) was a sensitive function of the hydrogen pressure (mtppms = meta-monosulfonated triphenylphosphine). This effect was attributed to the shift of the equlibrium between the known Ru(II)- monohydride: [RuHCl(mtppms)3] and a dihydride, supposedly [RuH2(mtppms)4], although it was also noted that a new hydride species was formed at slightly elevated pressure of H2 (5-10 bar). The situation is even more complicated since the formation of the various hydride species is also strongly influenced by the pH of the aqueous solutions.

Recently we made detailed 1H and 31P NMR studies in order to establish the effects of the pH and the hydrogen pressure on the reaction of [{RuCl2(mtppms)2}2] (+ mtppms) and H2, including the determination of T1 and T2 relaxation times. The results revealed the formation of the following complexes:

a)      in acidic solutions at 1 bar H2: [RuHCl(mtppms)3] and [{RuHCl(mtppms)2}2]

b)      in acidic solutions at elevated H2 pressures: trans-[RuH2(mtppms)4]

c)      in basic solutions at 1 bar H2: cis-[RuH2(H2O)(mtppms)3]

d)      in basic solutions at elevated H2 pressure: cis-[RuH2(H2)(mtppms)3]

Of these complexes, cis-[RuH2(H2)(mtppms)3] is a dihydrogen complex with water soluble phosphine ligands and trans-[RuH2(mtppms)4] is one of the rare trans-dihydrides. (Furthermore, cis-[RuH2(H2O)(mtppms)3] was previously incorrectly described as cis-[RuH2(mtppms)4].) 

 

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Presentation: Poster at COST D30 Final Evaluation Meeting, by Ferenc Joó
See On-line Journal of COST D30 Final Evaluation Meeting

Submitted: 2007-10-20 14:34
Revised:   2009-06-07 00:44